swarm-ci-runner: run the forge CI runner as a swarm service

The CI runner was a hive deploy module: hive-ci.nix ran it beside the
forge, and hive-c0re registered it through the forge's admin API with
the `core` token, writing the registration token through hive-priv. It
could only run on the forge's host, and it kept an admin-scoped forge
token on a hive.

Now the runner is a swarm service:

- swarm-ci-runner.nix runs it in a `swarm-ci-runner` container on the
  host that sets deploy.ci-runner.enable, reaching the forge by name.
  It needs neither the forge nor a hive there.
- swarm-controller reads the forge's runner registration token with its
  own admin token and writes it to swarm/services/ci-runner/
  registration-token whenever it differs from what it last wrote. Its
  grant on that path is create/update only.
- The runner's own leaf (CN swarm-ci-runner, role and policy of the same
  name) reads that one path. swarm-bao-ci-runner.service fetches it into
  the runner's EnvironmentFile and restarts the runner on a change.
- A pre-start step removes .runner when the daemon's journal since its
  last start holds Forgejo's "unregistered runner" refusal (the daemon
  exits 1 when its startup Declare gets it), or when .runner names
  another forge address; upstream's pre-start step then registers again.

Removed from the hive side: hive-ci.nix and deploy.forgejo.ci.*,
forge/ci_runner.rs, PrivRequest::RegisterCiRunner and its handler and
ReadWritePaths entry, InfraContainer::Ci with hivectl's --ci and the
dashboard's hive-ci journal entry, HYPERHIVE_FORGE_CI_ENABLED, and
read:admin,write:admin from CORE_TOKEN_SCOPES: nothing else in hive-c0re
calls /api/v1/admin/*. The old ci options, under both swarm.forge.ci and
deploy.forgejo.ci, now fail evaluation naming deploy.ci-runner.

The forge's half of the old ci.enable, the actions/checkout mirror and
DEFAULT_ACTIONS_URL = self, is deploy.forgejo.actionsFromSelf.

Closes #4954

docs/web-ui/dashboard.md

@@ -515,15 +515,15 @@ deep-link directly to a specific agent's journal. A "fetched N ago"
 chip appears after the `↻ refresh` button following each successful
 fetch and ticks every 30 s.
 
-**INFRA sub-tab** — journald viewer for the four hive infrastructure
-containers (`hive-ci`, `hive-forge`, `hive-gateway`, `hive-matrix`), a
+**INFRA sub-tab** — journald viewer for the three hive infrastructure
+containers (`hive-forge`, `hive-gateway`, `hive-matrix`), a
 fixed client-side list (`INFRA_NAMES` in `logs.js` — no dashboard API
 exposes just the name list). No unit filter (infra containers don't run
 the per-agent hive daemons) — always the full machine journal (or, for
 the gateway, the host journal filtered to its own unit). Fetches
 `GET /api/journal/{name}?lines=500`, same "fetched N ago" ticker as
 AGENT. A `?agent=<name>` deep-link routes here instead of AGENT when
-the name is one of the four infra containers.
+the name is one of the three infra containers.
 
 **SYSTEM sub-tab** — host-side service logs. Unit selector
 (`hive-c0re.service` / `hive-priv.service`). Fetches